The conventional process for formulating high melting point alloys from constituent materials through melting involves two stages. In the first stage, the non-reactive elements comprising a portion of the high melting point alloy are refined to remove as much oxygen and nitrogen as possible, usually through the addition of carbon to promote a carbon boil.
In the second stage, the elements which readily react with oxygen and nitrogen and comprise the reactive portion of the high melting point alloy are added to the non-reactive charge. The reactive elements are added late in the vacuum induction melt cycle so that the time these elements spend in the vacuum furnace is minimized to limit any reaction with the crucible lining and residual air in the furnace The reactive elements, however, must remain in the melt for a time sufficient to achieve homogenization. The reactive elements are added, for the most part, as elemental additions rather than mixtures or compounds of several reactive elements. Because allowances must be made to compensate for the wide variety in melting points and densities among the elemental additions, the conventional process for producing high melting point alloys is both time consuming and difficult to automate.
The conventional process suffers from the further disadvantage that exothermic reactions occur when particular reactive elements are added to the melt. For example, an exothermic reaction occurs when aluminum is added to a melt containing nickel. Such exothermic reactions cause high temperature excursions which accelerate the reaction of the melt with the refractory lining of the crucible, resulting in both shortened crucible life and also increased contamination in the high melting point alloy.
Accordingly, it is an object of the invention to provide a method of forming a high melting point alloy which overcomes the difficulties and disadvantages of the prior art.
Additional objects and advantages will be set forth in part in the description which follows, and in part, will be obvious from the description, or may be learned by practice of the invention.